Abstract: Please visit the following link for more details:http://cmb.physics.wisc.edu/journal/index.html
Please feel free to bring your lunch!
If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Le Zhang (lzhang263@wisc.edu)

Abstract: Please visit the following link for more details:http://cmb.physics.wisc.edu/journal/index.html
Please feel free to bring your lunch!
If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Le Zhang (lzhang263@wisc.edu)

Abstract: Our species has been around for 250,000 years or so. During nearly 249,800 of these, life expectancy at birth was steady at a level hovering around 25 years. But over the last 200 years, that is 0.1 percent of our species' lifetime on the planet, life expectancy at birth increased from about 25 years to about 80 years or, equivalently, Homo added 2.6 months of life per year. Some countries have cruised along with a pace of gains in survival twice as large as this average. It turns out that, on average and contrary to most past forecasts, life expectancy at birth has been going up linearly for a long time.

How did this happen? Can we keep it going? Aside from occasional setbacks (HIV, collapse of social organizations, wars, Ebola(?)) can one harbor the hope that by the year 2050 newborn cohorts will be expected to live 90-100 years? And if so, how healthy could the 90% of newborns who will make it to their 90th birthday expected to be? And what does this do to the course of human evolution?

Abstract: We study novel thermal Dark Matter (DM) scenarios where the annihilation of DM captured in the Sun produces boosted stable particles in the dark sector. These stable particles can be the annihilating DM itself, as in the scenario of semi-annihilating DM where DM possesses non-minimal stabilization symmetries, or can be a lighter subdominant DM component, as in the scenario of a multi-component DM sector. We investigate both of these possibilities and present concrete models as proofs of concept, considering DM mass in the wide range of O(1)-O(100) GeV. With a large Lorentz boost, these boosted DM can be detected in large volume terrestrial experiments, such as experiments designed for neutrino physics or proton decay searches, via neutral-current-like interactions with nuclei or electrons. In particular, we propose a search for proton tracks pointing towards the Sun, which is a primary detection channel for boosted DM from the Sun at neutrino experiments. We focus on studying the signals at Cherenkov-radiation-based detectors such as Super-Kamiokande (SK) and its upgrade Hyper-Kamiokande (HK). We find that with spin-dependent scattering as the dominant DM-nucleus interaction at low energies, boosted DM can leave detectable signals at SK or HK, while being consistent with current DM direct detection constraints. The boosted DM signal highlights the distinctive signatures that can arise in non-minimal DM sectors.

Abstract:
Non-Abelian anyons are widely sought for the exotic fundamental
physics they harbour as well as for their possible applications for
quantum information processing. Currently, there are numerous
blueprints for stabilizing the simplest type of non-Abelian anyon, a
Majorana zero energy mode bound to a vortex or a domain wall. One such
candidate system, a so-called "Majorana wire" can be made by
judiciously interfacing readily available materials; the experimental
evidence for the viability of this approach is presently emerging.
Following this idea, we introduce a device fabricated from
conventional fractional quantum Hall states, s-wave superconductors
and insulators with strong spin-orbit coupling. Similarly to a
Majorana wire, the ends of our “quantum wire” would bind
"parafermions", exotic non-Abelian anyons which can be viewed as
fractionalized Majorana zero modes.
I will briefly discuss their properties and describe how such
parafermions can be used to construct new and potentially useful
circuit elements which include current and voltage mirrors,
transistors for fractional charge currents and "flux capacitors".

Abstract: Part 1: The extragalactic gamma-ray background (EGB) is generated by the superposition of all extragalactic gamma-ray emissions and therefore provides a window on both the demographics and evolution of non-thermal phenomena across cosmic time. A significant fraction of the total EGB intensity has now been resolved into individual sources using the Fermi LAT, and there is an emerging understanding of how fainter members of the established extragalactic gamma-ray source classes can account for a majority of the residual approximately isotropic component of the gamma-ray sky, called the isotropic gamma-ray background (IGRB). The latest measurement of the IGRB spectrum with the Fermi LAT from 100 MeV to 820 GeV exhibits a high-energy cutoff feature consistent with the attenuation of high-energy gamma rays by pair-production on the IR/optical/UV extragalactic background light. High-energy cosmic neutrinos will be essential to see beyond this gamma-ray horizon to greater distances and higher energies.

Part 2: Targeted searches for indirect dark matter signals in the direction of Milky Way satellite galaxies provide some of the strongest current constraints on the annihilation cross section of dark matter derived from gamma-ray observations. Milky Way satellite galaxies have the advantages of low astrophysical backgrounds, the ability to constrain the dark matter abundance and distribution from the kinematics of member stars, and the opportunity to combine observations of multiple satellites in a joint-likelihood framework to enable more sensitive analyses. Accordingly, the discovery of additional Milky Way satellites in wide-field optical imaging surveys may provide substantial advances for indirect dark matter searches. I will discuss a matched-filter maximum-likelihood algorithm to search for and characterize ultra-faint galaxies in the ongoing Dark Energy Survey, which will cover 5000 square degrees in the relatively less explored south Galactic cap.

Abstract: As the nearest metal-rich, star-forming galaxy to the Milky Way, M31 plays a key role in understanding the interstellar medium (ISM) and star formation at z~0. Because of its proximity, we can study the properties of the ISM on the scale of individual star-forming molecular clouds and characterize the stellar sources of energy input for the ISM gas and dust. Recent observations have emphasized the importance cloud-scale processes in setting the efficiency of star formation. In particular, the formation of bound molecular clouds out of the cold neutral medium is a critical step in the process. Small spatial scale processes are also crucial for generating the tracers of star formation we use to study distant galaxies. M31 is currently the only metal-rich galaxy where existing observational facilities let us probe these important scales in all of the relevant tracers. Towards that end, we have assembled a powerful multi-wavelength observational dataset for a large portion of the disk of M31 - including HI 21-cm and radio continuum mapping from the VLA, CO J=(1-0) mapping from CARMA, Spitzer and Herschel photometry, Herschel spectroscopy, optical integral field spectroscopy, and resolved stellar photometry from the Pan-chromatic Hubble Andromeda Treasury (PHAT). I will summarize what we have learned about the connection between star formation and the ISM from this unique dataset.<br>

Speaker: Ken Freeman, ANU College of Physical and Mathematical Sciences

Abstract: The faintest dwarf galaxies are very baryon-depleted and have large
M/L ratios. Their gravitational fields are dominated by their dark halos.
If the dark halos have cores of near-constant surface density, and the
baryons have isotropic kinematics and are close to isothermal as observed,
then the density distribution of the baryons is expect to have a simple
analytic form which we can use to measure the central densities of their
dark halos. The observed density distributions of the faintest dwarf
spheroidal and dwarf irregular galaxies appear to follow this expected
distribution.

The core radii and central densities of the dark halos of rotationally
dominated late-type spirals scale with their absolute magnitudes: the
densities decrease with luminosity and the core radii increase, with
the central surface densities of the halos being almost independent of
lumiosity. I will talk about the consequences of these scaling laws and
some other correlations for the epoch of formation of the dwarfs, the
sizes of their dark halos and the existence of dark dwarfs.

Abstract: Progress in physics and quantum information science motivates much recent study of the behavior of extensively-entangled many-body quantum systems fully isolated from their environment, and thus undergoing unitary time evolution. What does it mean for such a system to go to thermal equilibrium? I will explain the Eigenstate Thermalization Hypothesis (ETH), which posits that each individual exact eigenstate of the system's Hamiltonian is at thermal equilibrium, and which appears to be true for most (but not all) quantum many-body systems. Prominent among the systems that do not obey this hypothesis are quantum systems that are many-body Anderson localized and thus do not constitute a reservoir that can thermalize itself. When the ETH is true, one can do standard statistical mechanics using the `single-eigenstate ensembles', which are the limit of the microcanonical ensemble where the `energy window' contains only a single many-body eigenstate. These eigenstate ensembles are more powerful than the traditional statistical mechanical ensembles, in that they can also "see" the quantum phase transition in to the localized phase, as well as a rich new world of phases and quantum phase transitions within the localized phase.